This invention relates to an article comprising a stack of sheets that may be applied, for example, to protect substrates such as glass or plastic windows, signage or displays.
Windows and glass in public transportation vehicles such as buses or subway trains can be subjected to a tremendous amount of abuse. The windows can be damaged by both incidental scratching during cleaning or they can be maliciously damaged by vandalism. Vandals damage the windows by scratching or abrading the surface of the window with items such as lava rock, diamonds, abrasive papers or abrasive cloths. Vandals can also damage the window by painting or coloring the surface of the window. Cleaning processes have been defined to eliminate damage by painting or coloring. However, scratching of glass by vandals presents a significant problem. In one major city, for example, approximately 40 percent of the bus windows have been vandalized by scratching and close to 80 percent of the subway train windows. The public transportation officials now call this type of graffiti xe2x80x9cscratchitixe2x80x9d. The best approach to stopping graffiti historically has been to remove the graffiti immediately once it appears. This graffiti prevention system which is known as xe2x80x9czero tolerancexe2x80x9d, has been extremely successful in eliminating the written and painted vandalism. Scratched glass, however, is extremely difficult and expensive to repair and as a result, the zero tolerance approach to scratchiti prevention and elimination is cost prohibitive. The vandalism issue tarnishes the overall image of an entire city""s transportation system. The vandalized glass leads to lower ridership because of the reduced perception of safety on the vehicle by the public. The vandalism ultimately leads to lost revenue for the public transportation system and substantially high repair costs.
Several approaches have been evaluated to combat the scrachiti problem. The first approach has been to repair the glass by a multi-step abrasion/polishing method to remove the scrachiti. The abrasion steps remove glass to the depth of the scratch with diamond abrasives and then with subsequently finer grades of diamond or aluminum oxide abrasives the surface of the glass is polished to its original appearance. The abrasive materials are expensive and the time required to completely abrade and polish the surface of the glass can be several hours depending on the depth of the damaged areas.
A second approach to eliminating the problem has been to apply a single permanent adhesive coated polyester sheet onto the surface of the window. The polyester sheet is thick enough to protect the window from scratching by diamonds, lava rocks and most abrasives. The sheet is typically applied onto the glass with a water solution to eliminate any trapped air. The application process takes about 5 to 10 minutes to complete. The sheet does a good job of protecting the window from most of the damage but the sheet is readily damaged and the damage is visible to the passengers. Removing the sheet is very time consuming taking about 15 to about 60 minutes depending on the amount of residue left on the window after removal of the sheet. Once the damaged sheet is removed, a new permanent adhesive coated polyester sheet needs to be applied. The time required to remove the adhesive coated polyester sheet, remove the adhesive residue from the glass, and apply a new permanent adhesive coated polyester sheet and reinstall the window can be close to 2 hours. Examples of single permanent adhesive coated polyester sheets which can be used to protect a window are 3M(trademark) Scotchshield(trademark) Safety and Security Window Film and 3M(trademark) Sun Control Window Films, data sheet number 70-0703-7220-0 published in September 1996 by the 3M Company.
The replaced sheet can be quickly damaged once the vehicle is used again in public thus necessitating another costly and time consuming replacement.
The third approach commonly used to repair and protect windows from scratches is to coat the damaged window with an epoxy coating. (Enhancement of Vehicle Glazing for Vandal Resistance and Durability, by Daniel R. Bowman, Mar. 25, 1996, available from the United States Transportation Research Board). The damaged window is typically first scrubbed clean before coating with an epoxy coating. The epoxy coating can be used to fill the defects on the windows and restore the window to a state of clarity where signs can be read through the window. To apply the coating, the window must be removed from the vehicle and the window must be cleaned and primed. The coatings are applied and cured in a clean environment. The coatings currently available however are easily scratched by the same method used to scratch the glass. Once the coating is damaged, it is difficult to apply a subsequent coating due to poor adhesion of the coating to the first layer. The process to replace the damaged coating with a new coating is time consuming and expensive.
Another approach to the problem is to apply a sacrificial window as a shield over an original non-damaged window. The vehicle""s window is modified with a frame that has a channel designed for a sheet of polycarbonate or acrylic. The rigid self-supporting sheet is inserted into the channel and acts as a barrier to damage on the base window. The polycarbonate sheet can be easily scratched by intentional methods being used to scratch the glass. This approach requires extensive modification to the window frame. Furthermore, the material cost per repair can be excessive making this approach cost prohibitive.
U.S. Pat. No. 3,785,102 discloses a pad comprising a plurality of very thin polyethylene or polypropylene removable sheets, each sheet bearing a very thin coating of pressure sensitive adhesive on its top surface for removing dirt from shoes and an adhesive at the bottom surface so that each successive layer is removably adhered to successive bottom layers and eventually to the floor. There is no discussion regarding the clarity of such a pad.
3M Masking and Packaging Systems Division sells a stack of sheets with adhesive that removes lint and pet hair under the trade names Pat It(trademark) Lint and Pet Hair Remover, product data sheet numbers 70-0705-7091-9, 70-0705-0819-0 and 70-0705-7038-0 published by 3M Company in 1994.
Research Disclosure 24109 (May 1984) discloses transmissive strippable plastic sheets stacked on mirror surfaces or stacked reflective (mirror surfaced) strippable plastic sheets that can be removed successively as toner or dust build up on the mirrors used in the optical imaging systems of electrophotographic reproduction apparatus occurs. The adhesive joining the layers to one another are provided only about the border areas of the sheets which are outside the optical image path to minimize image quality losses.
JP 10167765A describes a method of cleaning windows by the application of an optically clear sheet of plastic film on the inner and outer surface of the glass. The film is comprised of polyvinyl chloride, polyacrylic acid, polyester or polycarbonate. The plastic film is thin and only a single sheet of plastic is described on each side of the glass. The sheet is removed when the sheet becomes soiled.
U.S. Pat. No. 5,592,698 discloses a tear away lens stack for maintaining visibility through a transparent protective eye and face shield of a racing vehicle drivers helmet which includes a tab portion having projections formed thereon to assist in grasping the tab portion for rapid tear away. No adhesive is used in the stack; rather the lenses are clipped together.
The present invention provides an article comprising a stack of sheets wherein the sheets are designed to be removable from each other such that a fresh sheet can be exposed after a topmost sheet above is damaged and then removed. The stack of sheets includes a vertically staggered side edge that aids in the identification of the topmost sheet in the stack for removal thereof from the stack of sheets. The stack can be applied, for example, to the interior of bus or train windows to provide protection for the windows. As a sheet is damaged by graffiti artists, the topmost sheet of the article can be removed by trained maintenance personnel to reveal a clean undamaged sheet below.
The present invention provides an article comprising:
a stack of sheets, wherein each sheet independently comprises:
(a) a film, the film having a first side having a surface area, an opposite second side surface having a surface area;
(b) a bonding layer having a first side having a surface area and an opposite second side having a surface area, wherein the bonding layer is bonded via its first side to the second side of the film such that at least a center of the surface area of the second side of the film is in contact with the bonding layer, wherein at least about 50 percent of the surface area of the second side of the film has the bonding layer bonded thereto;
(c) an optional release layer coated on the first side of the film;
wherein each sheet is stacked upon another sheet such that except for a bottom sheet of the stack of sheets, the bonding layer of a sheet is in contact with the film or release layer, if present, of a sheet below;
wherein at least a portion of the side edges of the sheets are disposed in a vertically staggered arrangement with respect to one another thereby forming a vertically staggered side edge, and wherein the vertically staggered side edge includes indexing surfaces which allow for identification of a single sheet;
wherein a topmost sheet can be removed from the stack of sheets by pulling it away from the stack such that the sheet being removed from the stack as well as the sheets remaining with the stack do not delaminate;
wherein the stack of sheets when subjected to a visual acuity test using a 3 meter Snellen eye chart can allow an observer with 6 meter/6 meter vision to read a line on the eye chart which is indicative of about 6 meter/9 meter vision or better.
In a preferred embodiment of the article of the invention the article when subjected to a visual acuity test using a 3 meter Snellen eye chart can allow an observer with 6 meter/6 meter vision to read the line on the eye chart which is indicative of about 6 meter/6 meter vision or better.
In a preferred embodiment the first side of the film is not bonded to a bonding layer of the same sheet. In other words, preferably each sheet has a bonding layer coated on the second side of the film only.
In a preferred embodiment of the article of the invention the bonding layer is continuous.
In a preferred embodiment, the article of the invention when subjected to a 180xc2x0 Peel Adhesion to Glass test leaves substantially no residue (more preferably no residue) on the glass.
In a preferred embodiment of the article of the invention the stack of sheets is transparent.
In a preferred embodiment of the article of the invention each sheet has a penetration resistance of at least about 0.5 kg, even more preferably at least about 1 kg, even more preferably at least about 2 kg, even more preferably at least about 2.5, even more preferably at least about 3 kg, even more preferably at least about 3.5 kg, and most preferably about 4 kg.
With respect to the article of the invention preferably the maximum haze value of the stack of sheets is less than about 10 percent, more preferably less than about 5 percent, and most preferably less than about 3 percent.
In a preferred embodiment of the article of the invention at least about 80 percent (more preferably at least about 90 percent, and most preferably about 100 percent) of the surface area of the second side of the film has the bonding layer bonded thereto.
Preferably the article of the invention comprises at least about 2 sheets, more preferably about 3 to about 10 sheets.
In a preferred embodiment of the article of the invention the release layer is present and the release layer of each sheet has a Taber abrasion resistance of about 25 percent or less, more preferably about 10 or less, and most preferably about 2 or less according to ASTM D1044-76 after 100 cycles.
In a preferred embodiment of the article of the invention the bonding layer comprises a material selected from the group consisting of acrylics, rubbers, polyolefins, and mixtures thereof.
In a preferred embodiment of the article of the invention the bonding layer comprises a pressure sensitive adhesive.
In a preferred embodiment of the article of the invention the bonding layer has a thickness ranging from about 5 to about 150 microns, more preferably about 10 to about 25 microns.
In a preferred embodiment of the article of the invention the film has a thickness ranging from about 25 to about 4000 microns, more preferably about 50 to about 1000 microns.
In a preferred embodiment of the article of the invention the film comprises a material selected from the group consisting of polyester, polycarbonate, acrylic, polyurethanes, poly acetyl, polyolefin based ionomers, ethylene vinyl acetate polymers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, urethane acrylate polymers, epoxy polymers, epoxy acrylate polymers, and blends thereof.
In a preferred embodiment of the article of the invention the film further comprises of an additive selected from the group consisting of ultraviolet light absorbers, ultraviolet light stabilizers, flame retardants, smoke suppressants, antioxidants, and mixtures thereof.
In a preferred embodiment of the article of the invention the film comprises multiple layers.
In a preferred embodiment of the article of the invention each sheet has a tensile strength of about 20 to about 2000 kP, an elongation of about 5 to about 1000% and a tear strength of about 0.05 to about 5 kg. Even more preferably each sheet has a tensile strength of about 70 to about 1400 kP, an elongation of about 5 to about 500% and a tear strength of about 0.5 to about 2.5 kg. Most preferably each sheet has a tensile strength of about 350 to about 1000 kP, an elongation of about 20 to about 100% and a tear strength of about 1.5 to about 2.5 kg.
In a preferred embodiment of the article of the invention the release layer is present.
In a preferred embodiment of the article of the invention the release layer has a thickness ranging from about 0.1 to about 25 microns, more preferably about 2.5 to about 5 microns.
In a preferred embodiment of the article of the invention the release layer comprises a material selected from the group consisting of acrylates, methacrylates, urethanes, silicones, polyolefins, fluorocarbons and mixtures thereof.
In a preferred embodiment of the article of the invention the bonding layer of each sheet further comprises a component selected from the group consisting of flame retardents, smoke suppressants, antioxidants ultraviolet light absorbers, ultraviolet light stabilizers, and mixtures thereof.
In a preferred embodiment of the article of the invention the sheets are rectangular sheets of the same length and width.
In a preferred embodiment of the article of the invention the vertically staggered side edge is located at an edge of said article.
In a preferred embodiment of the article the vertically staggered side edge is located at a corner of said article.
In a preferred embodiment of the article the indexing surfaces have a shape selected from the group consisting of crescent shaped, rectangular, semicircular, and trapezoidal.
In a preferred embodiment of the article the vertically staggered side edge is positioned at a corner of said article and the indexing surfaces are crescent shaped having one concave edge and one convex edge.
In a preferred embodiment of the article the vertically staggered side edge has a width ranging from about 0.5 mm to 25 mm and has a length ranging from about 25 mm to about 50 cm although the length of the vertically staggered side edge may also extend along the entire length of an edge of the article.
In a preferred embodiment of the article the vertically staggered side edge is in a staircase configuration or a reverse staircase configuration.
The present invention also provides a construction comprising:
(i) an article comprising:
a stack of sheets, wherein each sheet independently comprises:
(a) a film, the film having a first side having a surface area and an opposite second side having a surface area;
(b) a bonding layer having a first side having a surface area and an opposite second side having a surface area, wherein the bonding layer is bonded via its first side to the second side of the film such that at least a center of the surface area of the second side of the film is in contact with the bonding layer, wherein at least about 50 percent of the surface area of the second side of the film has the bonding layer bonded thereto, wherein with respect to each sheet the first side of the film is not bonded to a bonding layer of the same sheet;
(c) an optional release layer coated on the first side of the film;
wherein each sheet is stacked upon another sheet such that except for a bottom sheet of the stack of sheets, the bonding layer of a sheet is in contact with the protective film or release layer, if present, of a sheet below;
wherein at least a portion of the side edges of the sheets are disposed in a vertically staggered arrangement with respect to one another thereby forming a vertically staggered side edge, and wherein the vertically staggered side edge includes indexing surfaces which allow for identification of a single sheet;
wherein a topmost sheet can be removed from the stack of sheets by pulling it away from the stack such that the sheet being removed from the stack as well as the sheets remaining with the stack do not delaminate;
wherein the stack of sheets when subjected to a visual acuity test using a 3 meter Snellen eye chart can allow an observer with 6 meter/6 meter vision to read a line on the eye chart which is indicative of about 6 meter/12 meter vision or better; and
(ii) a substrate to which the article is bonded via the bonding layer of the bottom sheet.
In a preferred embodiment of the article of the invention the substrate comprises a material selected from the group consisting of glass, metal, plastic, painted surfaces, wood, fabric, wallpaper, ceramic, concrete, mirrored surfaces, plastic/glass laminates, and combinations thereof.
In a preferred embodiment of the article of the invention the substrate is part of a structure. Most preferably the structure is selected from the group consisting of windows, walls, partitions, signs, bill boards, artwork, buildings, elevators, vehicles, furniture, doors. CRT displays, personal computer/organizer screens, touch screens, and membrane switches.
In a preferred embodiment of the construction
the structure comprises a vehicle comprising a window;
and the article is bonded via the bonding layer of the bottom sheet to the window. Most preferably the vehicle is selected from the group consisting of buses, trains, and subways.
The present invention also provides a method comprising the steps of:
(a) applying an article as described above to a substrate via the bonding layer of the bottom sheet of the article;
(b) allowing the topmost sheet of the article to be damaged;
(c) removing the damaged topmost sheet of the article by identifying the topmost sheet in the stack with reference to the indexing surface and gripping the topmost sheet and pulling it away from the stack, in a manner such that neither the sheet being removed nor the stack of sheets which remains delaminates, in order to expose a lower sheet of the article which becomes the topmost sheet of the article.
In a preferred embodiment of the method, steps (b) and (c) are repeated at least once. More preferably steps (b) and (c) are repeated until the bottom sheet is removed, and the bottom sheet upon removal leaves substantially no adhesive residue (most preferably) on the substrate.